Viruses and viral diseases of salmonids

Abstract

Salmonid fishes are one of the most important aquatic resources in the world, and since salmonid fish culture was initiated many years ago, it has been developing with the times in several countries. In particular, the intensive culture of rainbow trout, Oncorhynchus mykiss, has developed over the past 30 years in the USA, Europe, Japan and elsewhere. However, the successes achieved have brought with them diverse new disease problems for rainbow trout and other salmonids. The crucial problems are communicable or infectious diseases caused by bacterial and viral agents, among which viral disease is the most serious, because diagnosis is difficult, the majority of the epizootics is acute or subacute, and furthermore, no chemotherapy is available for them. The viral agents, the viral infections and the pathologic conditions of salmonid fishes can be grouped into the respective viral families according to the attributes of the virus, and into an unclassified virus group as follows. RNA VIRUS GROUP: Birnaviridae, Paramyxoviridae, Picornaviridae, Reoviridae ( Reovirus and Rotavirus), Retroviridae, Rhabdoviridae, and Togaviridae: DNA VIRUS GROUP: Adenoviridae, Herpesviridae and Iridoviridae. In addition to the viral diseases which have been internationally recognised, this review gives new information on other diseases including Salmonid Picornalike Viruses, Landlocked Salmon Virus (LSV), Atlantic Salmon Rotavirus (ASR), Trout Strawberry Disease (TSD), Coho Salmon Tumor Virus (CSTV), Epizootic Epitheliotropic Disease of Lake Trout, Epizootic Hematopoietic Necrosis (EHN) of Trout, Erythrocytic Inclusion Body Syndrome (EIBS). Intraerythrocytic Viruslike Particles different from EIBS in Atlantic Salmon, and Third Erythrocytic Virus associated with anemia. Among these, the pathologic conditions from which a causative virus has been isolated are Coho Salmon Tumor, Epizootic Hematopoietic Necrosis of Trout, Trout Strawberry Disease, Atlantic Salmon Rotavirus Disease, and Landlocked Salmon Virus Disease. Furthermore, Salmonid Picornalike Virus and Cutthroat Trout Virus have been isolated from the asymptomatic condition. The rest are viral infections with the viruses visualized but not yet isolated. This article deals with over twenty viruses, viral diseases and pathologic conditions of salmonids.